1. Field of the Invention
The present invention relates to a control method for display data, more particularly, relates to a data display control method to display compressed data from a data server in a network at high speed.
2. Description of the Related Art
As internet and the like come into wide use and a personal computer has a high performance in recent years, structured languages carrying out a three-dimensional virtual space (Virtual Reality Modeling Language: hereinafter, called VRML) come into wide use. In this system, the VRML is used for programming to structure a three-dimensional space, and then is stored in a server. A user accesses data stored in the server by a viewer to restructure the three-dimensional space from the VRML, and then the user restructures the three-dimensional space by a personal computer. With this arrangement, the user can walk through the three-dimensional space freely.
There has started to be use a virtual mall in which shops are open in this virtual space, and such a virtual space is shown in "Three-Dimensional Interactive Space AGORA linked to WWW, Harada et al., Joint Workshop of MIS.cndot.NA.cndot.OFS Study Groups in Electronics Information Communication Society, Sapporro, 18-19.9.1995".
The following is an outline to display a three-dimensional space.
First, VRML data are stored into a server in a network. When a server name and a VRML data are designated by a viewer set at a client, the client accesses the designated VRML data in the server, and receives the VRML data. Then, the client restructures the three-dimensional space with the received VRML data, whereby the user can walk through in this three-dimensional space freely. Further, to structure the three-dimensional space really, it is possible to structure the three-dimensional image close to the original by using a pattern image (texture image) on a surface of a three-dimensional object. When a capacity for the VRML data and the texture data becomes large, to reduce a communication time in a network, compressed data is stored in the server by using various data compression technology, and then the compressed data is decompressed by the client, whereby a three-dimensional image is displayed.
FIG. 15 shows an outline of a display control method between a server and a display client in the conventional network. As shown in FIG. 15, a server S and a client C are connected to each other via a network NW. In the server S, compressed data (VRML(.wrl.gz.), JPEG(.jpg)) is held. The compressed data held in a data hold part 21 is transmitted from a data supply part 22 to meet data requests from the client C.
A data request part 23 in the client C requires the server S to send data, and receives compressed data transmitted from the server S. Then, a data hold part 24 holds the compressed data once. Successively, when display is required, the data request part 23 reads compressed data required for display from the data hold part 24 and sends the data to a data decompression part 25. The data decompression part 25 decompresses the compressed data, and then transmits decompressed data to a three-dimensional display processing part 26. The three-dimensional display processing part 26 generates data for display, and transmits the data to a display unit not shown.
As shown in FIG. 15, conventionally, the client C is provided with the data hold part 24 for holding data received from the server S. When the following scene is similar to that already displayed, the scene is displayed with the data held in the data hold part 24. The data once received is held in the data hold part 24 in this way and is used, whereby a data transmitting time from the server S is reduced and a three-dimensional display process is carried out at high speed. In this case, data instructing display corresponds to a data name held in the data hold part 24.
When the data name instructed to be displayed indicates compressed data, the data hold part 24 also keeps the compressed data. When the three-dimensional display is performed, the compressed data held in the data hold part 24 is decompressed, and then is displayed.
For example, an image data processing system disclosed in Japan Patent Application Laid-Open No. 62-6854 in 1987 is provided with two compressed data caches, whereby data are transmitted at high speed in the system. In this system, compressed data are held in the data caches to improve a transmitting speed.
Further, structured data in which a number of texture pixels varies in accordance with distance data (Level of Detail: hereinafter, called LOD) are prepared, and various data are required in accordance with the LOD from the client C. That structure is shown in FIG. 16.
As shown in FIG. 16, compressed data are held by a data hold part 21a in the server S similarly to those in FIG. 15, namely, each compressed data is held in accordance with the value of the LOD. In FIG. 16, there are three cases in that the LOD is not more than 100, from 100 to 200, and not less than 200, compressed data which each corresponding image is compressed is held.
The client C requires the server S to transmit data corresponding to the LOD, whereby image data corresponding to the transmitted LOD is read from the data hold part 21a. The following processes are similar to those in FIG. 15.
Not many texture images are used for a far primitive, and many texture images are used for a close primitive. Although it is necessary to prepare plural data for the same primitive, a far primitive can be displayed with a little data quantity. Thus, it is possible to reduce the transmitting time and to carry out the display process at high speed.
Concerning the technology in that the data obtained by accessing the server S is stored in the data caches and the stored data is used for the following display, however, there is a possibility that the following problems occur. That is, the data stored in the data caches is kept as it is whether the data is compressed data or non-compressed data. Thus, when the data stored in the data caches is compressed data, it is necessary to apply the decompression process to the data for the display process every time, therefore, there is a problem to lower the speed of the display process.
Moreover, concerning the method in that the display is made high speed by requiring various data corresponding to the distance data LOD, it is necessary to prepare plural programmed data for one three-dimensional object in accordance with distances. Thus, it is necessary to prepare plural data to carry out high speed display.